This invention relates to mining machines, primarily though not exclusively intended for coal mines, and relates particularly to machines known as continuous miners.
Known methods of mining coal include board and pillar mining, and longwall mining. In longwall mining, entries or roads are driven about 200 meters apart. A coal face is formed between the roads either at the starting points of the roads in the longwall advancing method or at the end of the roads in the longwall retreating method. In the longwall advancing method, the face is mined traversing the face and shearing off a certain depth from the face. Under repeated traversals, the face advances in the direction of the roads. In the longwall retreating method, the method of mining is the same except that mining starts from the ends of the roads and the face retreats in the reverse direction of the roads.
A common type of machine employed for longwall mining is known as the Anderson shearer and comprises two cutter drums rotating parallel to the face at each end of a carriage. Both drums act to cut into the face and shear off coal as the machine is moved across the entire length of the face.
In board and pillar mining, a board or area of coal is mined and pillars of coal are left at intervals to support the roof. A machine known as the continuous miner has been developed for cutting out the coal in board and pillar mining. The term "continuous miner" arises because the machine can cut continuously without requiring shot firing of the coal face, in contrast to earlier types of machines. A continuous miner is a versatile type of machine and can also be used for cutting roads and is useful in cutting breakaway routes and air vents from existing roads.
A common form of continuous miner is shown schematically in FIGS. 1 and 2. It comprises a chassis 2 with a personnel cabin 4 mounted for free movement by means of crawler tracks 6. At the front end is mounted a cutting head 8 mounted with its axis parallel to the coal face on pivot arm 10. Arm 10 is raised and lowered by hydraulic rams 12. A loading apron 14 is provided at ground level beneath cutting head 8, apron 14 including a conveyor 16 which extends along the body 2 to communicate with a loading jib 18 for disposing of cut coal. In operation the cutting head is pivoted up and down to cut the face and the cut coal is gathered up by the conveyor. In order to cut across a face which is wider than the machine, the machine is slewed across the face by means of the crawler tracks.
In order to break away from an existing road way or to form an air vent, the miner is angled towards the side of the road (the road is only 5.5 m wide, and the miner cannot be manoeuvred sideways on), and the cutting head cut into the side of the road in a series of advance and reversing motions of the miner.
A problem with all types of mining is to reinforce the roof of the mine subsequent to cutting the coal. Various types of machine are available for providing reinforcement, but a very common method of reinforcing is to insert roof bolts into drilled holes in the roof. The roof bolts are secured in the drilled holes and a nut on the projecting end of the bolt tightened. This acts to reinforce the surrounding rock.
Roof bolts are commonly used when operating a continuous miner and frequently the miner itself may be equipped to drill holes in the roof. As shown in FIGS. 1 and 2, the miner has roof drills 20 one on either side of pivot arm 10. In order to operate these drills, the cutting head 8 is stopped in operation and the drilling operation is carried out.
A disadvantage with this arrangement is the relatively large distance between the cutting head and the roof drills which may be as great as 4 m. Thus in areas where the roof is loose, there may be an unstable region relatively large in extent.